title: Photodegradation of folate sensitized by riboflavin.
abstract: Folate is shown to react with singlet-excited state of riboflavin in a diffusion controlled reaction and with triplet-excited state of riboflavin in a somewhat slower reaction with (3)k(q) = 4.8 × 10(8) L mol(-1) s(-1) in aqueous phosphate buffer at pH 7.4, ionic strength of 0.2 mol L(-1), and 25°C. Singlet quenching is assigned as photo-induced reductive electron transfer from ground state folate to singlet-excited riboflavin, while triplet quenching is assigned as one-electron transfer rather than hydrogen atom transfer from folate to triplet-excited riboflavin, as the reaction quantum yield, φ = 0.32, is hardly influenced by solvent change from water to deuterium oxide, φ = 0.37. Cyclic voltammetry showed an irreversible two-electron anodic process for folate, E = 1.14 V versus NHE at a scan-rate of 50 mV s(-1), which appears to be kinetically controlled by the heterogeneous electron transfer from the substrates to the electrode. Main products of folate photooxidation sensitized by riboflavin were pterin-6-carboxylic acid and p-aminobenzoyl-L-glutamic acid as shown by liquid chromatographic ion-trap mass spectrometry (LC-IT-MS).
authors.affiliation: Instituto de Quimica de São Carlos, Universidade de São Paulo, São Carlos, São Paulo, Brazil.
authors.forename: Regina S
authors.initials: RS
authors.lastname: Scurachio
authors.forename: Leif H
authors.initials: LH
authors.lastname: Skibsted
authors.forename: Gustavo
authors.initials: G
authors.lastname: Metzker
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Cardoso
mesh_terms: D002853:Chromatography, Liquid; D003217:Conductometry; D004579:Electron Transport; D004583:Electrons; D005492:Folic Acid / Q000737:chemistry* / Q000378:metabolism; D005971:Glutamates / Q000138:chemical synthesis*; D006863:Hydrogen-Ion Concentration; D008027:Light; D013058:Mass Spectrometry; D010084:Oxidation-Reduction / Q000528:radiation effects; D010777:Photochemistry / Q000379:methods*; D010782:Photolysis / Q000528:radiation effects; D011621:Pteridines / Q000138:chemical synthesis*; D012256:Riboflavin / Q000737:chemistry* / Q000378:metabolism; D012997:Solvents; D013816:Thermodynamics; D014867:Water
chemical_list: D005971:Glutamates; D011621:Pteridines; D012997:Solvents; C405202:pterine-6-carboxylic acid; D014867:Water; D005492:Folic Acid; C011398:4-aminobenzoylglutamic acid; D012256:Riboflavin